A new study of seven kittens suggests a new treatment for amblyopia or “lazy eye” in humans. The kittens did not themselves have the disorder (in which one eye works but the connections between it and the brain are disrupted). It was induced via a procedure called monocular deprivation, in which one of the eyelids of each kitten was sewn shut 30 days after birth, a critical period for the development of vision.
The kittens all, thankfully, regained their vision. That is, the proposed treatment for amyblopia — placing them in total darkness for ten days straight — was successful. While monocular deprivation “does no lasting harm to the kittens’ eyes or eyelids” according to NPR, the kittens did have to undergo painful procedures that are simply not be thinkable to carry out on humans.
In the experiment, a week after the surgery, the kittens’ eyes were reopened and they were found to be unable to see out of one eye. They were placed in total darkness, some right after having their eyes re-opened and others for five to eight weeks. The kittens who were immediately placed in the darkness regained their vision after seven weeks. But the others, whose “treatment” was delayed, regained their vision after five to seven days.
The Dalhousie University scientists who conducted the experiment attribute the kittens being able to get their eyesight back to their brains’ visual system being in an early stage of development. Young kittens have low levels of a protein called neurofilaments while older cats have more. Neurofilaments are described as”rigid scaffolding” in the brain and are thought to reduce its plasticity. Young kittens’ brains are therefore more able to adapt and change than those of adults.
Amblyopia in human children is now usually treated by placing a patch over the dominant eye, to make the “lazy eye” get stronger. There are side effects, such as the loss of depth perception and a weakening of the dominant eye. (Anecdotally, my late mother-in-law, sister-in-law and niece all had a lazy eye and wore a patch, with no lasting side effects.)
As NPR observes a bit tongue-in-cheekily, scientists emphasize that immersion-in-darkness as a potential treatment for lazy eye in humans is not even being considered and that “we shouldn’t start throwing children into the dark just yet.” The logistics — having a child stay in total darkness for a period of days — would certainly be complicated.
While it is a huge relief to know that the kittens in the experiment all regained their eyesight, it is an understatement to say that the study raises huge ethical questions. There is a need to study the brain and how it functions to develop new treatments. But knowing that kittens were deliberately blinded and placed in the dark for days to make new discoveries casts a shadow over the study and its findings.
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